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Abstract:

A solar window apparatus for collecting solar energy and regulating light
transmission is provided in which the solar window comprises a plurality
of transparent optical elements adhered to an internal surface of a
transparent pane. The optical elements each comprise an externally facing
surface and an internally facing light collecting surface with a light
collecting element adhered thereto, where the externally facing surface
preferably has an area that is larger than that of the light collecting
surface. Each optical element further comprises two or more light
directing surfaces that internally reflect and concentrate light onto the
light collecting elements when light is incident over a first range of
angles, and transmit light when light is incident over a second range of
angles.

Claims:

1. A hybrid solar energy collection and light regulation apparatus
comprising: a substantially transparent pane; a plurality of
substantially transparent optical elements adhered to an internal surface
of said pane, wherein light directed onto an external surface of said
pane is substantially transmitted through said pane and substantially
transmitted through an externally facing surface of each optical element;
each optical element further comprising: an internally facing light
collection surface having adhered thereto a light collection element; and
two or more light directing surfaces; wherein said light directing
surfaces are oriented to reflect a portion of said light transmitted
through said externally facing surface when said light is incident upon
said pane within a first range of angles, and to transmit a portion of
said light transmitted through said externally facing surface when said
light is incident upon said pane within a second range of angles; and
wherein at least two of said light directing surfaces are located on
opposing sides of said each optical element.

2. The apparatus according to claim 1 further comprising an internal
optical diffusing component.

3. The apparatus according to claim 1 wherein said substantially
transparent pane is an external pane, said apparatus further comprising a
substantially transparent internal pane, said external and internal panes
forming a double-pane window wherein said optical elements are located
between said internal and external panes.

4. The apparatus according to claim 3 wherein said internal pane is an
optically diffusing pane.

5. The apparatus according to claim 1 wherein heat absorbed by said light
collection elements is substantially thermally conducted to said pane.

6. The apparatus according to claim 1 further comprising a heat sink
means in thermal communication with one or more of said light collection
elements.

7. The apparatus according to claim 6 wherein said heat sink means
comprises a liquid conduit thermally contacting one or more of said light
collection elements.

8. The apparatus according to claim 7 further comprising a flow means for
flowing said liquid through said conduit.

9. The apparatus according to claim 7 wherein said conduit is
substantially transparent.

10. The apparatus according to claim 1 wherein said optical elements are
adhered to said internal surface of said pane without an air gap
therebetween.

11. The apparatus according to claim 1 wherein said optical elements are
provided in an array.

12. The apparatus according to claim 1 wherein said externally facing
surface is larger in area than said light collecting surface.

13. The apparatus according to claim 12 wherein each optical element
comprises a prism, wherein said externally facing surface, said light
collecting surface, and said light directing surfaces are sides of said
prism, said sides having an axis parallel to a longitudinal axis of said
prism.

14. The apparatus according to claim 13 wherein said prisms are arranged
in a one-dimensional array.

15. The apparatus according to claim 13 wherein one or both ends of said
prism are cut at an angle relative to a plane orthogonal to a
longitudinal axis of said prism.

16. The apparatus according to claim 15 wherein said prism is a
quadrilateral prism.

17. The apparatus according to claim 16 wherein said prism comprises a
trapezoidal cross-section.

18. The apparatus according to claim 12 wherein said optical element
comprises a truncated pyramid, wherein said light collecting surface
comprises a truncated surface of said pyramid.

19. The apparatus according to claim 18 wherein a base of said pyramid is
additionally truncated at an oblique angle, wherein said light collecting
surface is oriented at an angle relative to said a substantially
transparent pane.

20. The apparatus according to claim 18 wherein said optical elements
comprise a two-dimensional array.

21. The apparatus according to claim 1 wherein one or more of said light
directing surfaces comprise a coating that is partially reflective.

22. The apparatus according to claim 13, said apparatus mounted in a
vertical orientation wherein said longitudinal axis is oriented in a
substantially vertical direction, wherein sunlight is partially
transmitted by a first light directing surface during a first time
duration during a day, and is partially transmitted by second light
directing surface during a second time duration during said day.

23. The apparatus according to claim 1, wherein each light collection
element comprises a solar cell, said apparatus further comprising
connection means for electrically connecting said solar cells.

24. The apparatus according to claim 23 wherein each solar cell is
connected to each light collection surface without an air gap
therebetween.

25. The apparatus according to claim 1, wherein said light collecting
element comprises an absorbing medium.

26. The apparatus according to claim 25 wherein said absorbing medium
comprises a light absorbing coating applied to said light collecting
surface.

27. The apparatus according to claim 1 further comprising a retrofitting
kit, said kit comprising fastening means for securing said substantially
transparent pane relative to an internal surface of a window.

28. A window retrofitted with an apparatus according to claim 1.

29. A skylight comprising an apparatus according to claim 1.

30. A light regulation apparatus comprising: a substantially transparent
pane; a plurality of substantially transparent optical elements adhered
to an internal surface of said pane, wherein light directed onto an
external surface of said pane is substantially transmitted through said
pane and substantially transmitted through an externally facing surface
of each optical element; each optical element further comprising: an
internally facing surface comprising a coating that is at least partially
reflective; and two or more light directing surfaces; wherein said light
directing surfaces are oriented to reflect a portion of said light
transmitted through said externally facing surface when said light is
incident upon said pane within a first range of angles, and to transmit a
portion of said light transmitted through said externally facing surface
when said light is incident upon said pane within a second range of
angles; and wherein at least two of said light directing surfaces are
located on opposing sides of said each optical element.

31. The apparatus according to claim 30 wherein one or more of said two
or more light directing surfaces comprise an additional coating that is
at partially reflective.

32. A light regulation apparatus comprising: a substantially transparent
pane; a plurality of substantially transparent optical elements adhered
to an internal surface of said pane, wherein light directed onto an
external surface of said pane is substantially transmitted through said
pane and substantially transmitted through an externally facing surface
of each optical element; wherein each optical element further comprises
two or more light directing surfaces; wherein said light directing
surfaces are oriented to reflect said light transmitted through said
externally facing surface when said light is incident upon said pane
within a first range of angles, and to transmit said light transmitted
through said externally facing surface when said light is incident upon
said pane within a second range of angles.

33. The apparatus according to claim 32 further comprising an internal
optical diffusing component.

34. The apparatus according to claim 32 wherein said substantially
transparent pane is an external pane, said apparatus further comprising
an internal substantially transparent pane, said external and internal
panes forming a double-pane window wherein said optical elements are
located between said external and internal panes.

35. The apparatus according to claim 34 wherein said internal pane is an
optically diffusing pane.

36. The apparatus according to claim 32 wherein said optical elements are
adhered to said internal surface of said pane without an air gap.

37. The apparatus according to claim 32 wherein said optical elements are
provided in an array.

38. The apparatus according to claim 32 wherein each optical element
comprises a prism, wherein said externally facing surface and said light
directing surfaces are sides of said prism, said sides having an axis
parallel to a longitudinal axis of said prism.

39. The apparatus according to claim 38 wherein said prisms are arranged
in a one-dimensional array.

40. The apparatus according to claim 38 wherein one or both ends of said
prism are cut at an angle relative to a plane orthogonal to a
longitudinal axis of said prism.

41. The apparatus according to claim 40 wherein said prism is a
triangular prism.

42. The apparatus according to claim 32 wherein one or more of said light
directing surfaces comprise a coating that is at least partially
reflective.

43. The apparatus according to claim 38, said apparatus mounted in a
vertical orientation wherein said longitudinal axis is oriented in a
substantially vertical direction, wherein sunlight is partially
transmitted by a first light directing surface during time duration
during a day, and is partially transmitted by second light directing
surface during a second time duration during said day.

44. A skylight comprising an apparatus according to claim 32.

45. A hybrid solar energy collection and light regulation apparatus
comprising: a substantially transparent first pane; a plurality of
lensing elements positioned adjacent to an internal surface of said pane,
wherein light directed onto an external surface of said pane is
substantially transmitted through said pane and substantially transmitted
through said lensing elements; a second substantially transparent pane
having an externally facing surface located approximately at a focal
plane of said lensing elements, said externally facing surface supporting
a plurality of light collecting elements, wherein each light collecting
element is positioned approximately at a focal point of a given lensing
element; wherein a substantial portion of said light transmitted through
said lensing elements is collected by said light collection elements when
said light is incident upon said first pane within a first range of
angles, and wherein a substantial portion of said light transmitted
through said lensing elements is transmitted through said second pane
when said light is incident upon said first pane within a second range of
angles.

46. The apparatus according to claim 45 wherein said lensing elements are
cylindrical lenses plano-convex lenses.

47. The apparatus according to claim 45 wherein said lensing elements are
cylindrical Fresnel lenses.

48. The apparatus according to claim 45 wherein said lensing elements are
adhered to said first pane without an air gap therebetween.

49. The apparatus according to claim 45 wherein said second pane is an
optically diffusing pane.

[0003] Solar cells may be incorporated into building windows such that
sunlight incident on the window can both generate electrical power and
simultaneously provide illumination for the interior of the building.
Windows of this type are known in the art and a trade-off exists between
the amount of illumination and the amount of electrical power generated.
Standard solar windows embed conventional solar cells into the window
which provides poor lighting quality in the building as well as only a
limited amount of solar energy.

[0004] Other solar window designs known in the art have similar
limitations. Thin film semitransparent windows only offer approximately
4-5% conversion efficiency. Windows which use silicon wafer-based solar
cells with gaps between cells to allow light transmission produce highly
non-uniform lighting which is distracting and makes poor task lighting.
In addition, these windows only allow a fixed percentage of window
illumination through, and this percentage must be fixed despite a wide
range of illumination conditions.

[0005] US Patent Application No. 20080271776 (Morgan) provides a design in
which an array of transparent triangular prisms is mounted on a
transparent pane, where one side of each prism comprises a solar cell.
This device is designed to maximize the amount of collected direct
sunlight, while allowing scattered light at low inclination angles to be
viewed. This design unfortunately does not address the need to modulate
the amount of direct incident light to accommodate for daily and seasonal
variations in solar illumination conditions. Furthermore, the design is
limited to vertical windows and is not adapted for use with horizontal
windows such as skylights.

[0006] What is therefore needed is a design that enables the collection of
light onto a solar collector while modulating the direct transmitted
sunlight during daily and seasonal variations, in a module adaptable for
a wide range of inclinations.

SUMMARY OF THE INVENTION

[0007] Embodiments of the present invention address the aforementioned
need by providing a solar window that regulates the transmission of light
over a wide range of incident angles by substantially transmitting the
incident light over a first range of angles and collecting and
concentrating the incident light onto collecting elements over a second
range of angles.

[0008] Accordingly, in a first aspect of the invention, there is provided
a hybrid solar energy collection and light regulation apparatus
comprising:

[0009] a substantially transparent pane;

[0010] a plurality of substantially transparent optical elements adhered
to an internal surface of the pane, wherein light directed onto an
external surface of the pane is substantially transmitted through the
pane and substantially transmitted through an externally facing surface
of each optical element;

[0011] each optical element further comprising: [0012] an internally
facing light collection surface having adhered thereto a light collection
element; and [0013] two or more light directing surfaces;

[0014] wherein the light directing surfaces are oriented to reflect a
portion of the light transmitted through the externally facing surface
when the light is incident upon the pane within a first range of angles,
and to transmit a portion of the light transmitted through the externally
facing surface when the light is incident upon the pane within a second
range of angles; and

[0015] wherein at least two of the light directing surfaces are located on
opposing sides of the each optical element.

[0016] In another embodiment, there is provided a light regulation
apparatus comprising:

[0017] a substantially transparent pane;

[0018] a plurality of substantially transparent optical elements adhered
to an internal surface of the pane, wherein light directed onto an
external surface of the pane is substantially transmitted through the
pane and substantially transmitted through an externally facing surface
of each optical element;

[0019] each optical element further comprising: [0020] an internally
facing surface comprising a coating that is at least partially
reflective; and [0021] two or more light directing surfaces;

[0022] wherein the light directing surfaces are oriented to reflect a
portion of the light transmitted through the externally facing surface
when the light is incident upon the pane within a first range of angles,
and to transmit a portion of the light transmitted through the externally
facing surface when the light is incident upon the pane within a second
range of angles; and

[0023] wherein at least two of the light directing surfaces are located on
opposing sides of the each optical element.

[0024] In yet another embodiment, there is provided a light regulation
apparatus comprising:

[0025] a substantially transparent pane;

[0026] a plurality of substantially transparent optical elements adhered
to an internal surface of the pane, wherein light directed onto an
external surface of the pane is substantially transmitted through the
pane and substantially transmitted through an externally facing surface
of each optical element;

[0027] wherein each optical element further comprises two or more light
directing surfaces;

[0028] wherein the light directing surfaces are oriented to reflect the
light transmitted through the externally facing surface when the light is
incident upon the pane within a first range of angles, and to transmit
the light transmitted through the externally facing surface when the
light is incident upon the pane within a second range of angles.

[0029] In another embodiment, there is provided a hybrid solar energy
collection and light regulation apparatus comprising:

[0030] a substantially transparent first pane;

[0031] a plurality of lensing elements positioned adjacent to an internal
surface of the pane, wherein light directed onto an external surface of
the pane is substantially transmitted through the pane and substantially
transmitted through the lensing elements;

[0032] a second substantially transparent pane having an externally facing
surface located approximately at a focal plane of the lensing elements,
the externally facing surface supporting a plurality of light collecting
elements, wherein each light collecting element is positioned
approximately at a focal point of a given lensing element;

[0033] wherein a substantial portion of the light transmitted through the
lensing elements is collected by the light collection elements when the
light is incident upon the first pane within a first range of angles, and
wherein a substantial portion of the light transmitted through the
lensing elements is transmitted through the second pane when the light is
incident upon the first pane within a second range of angles.

[0034] A further understanding of the functional and advantageous aspects
of the invention can be realized by reference to the following detailed
description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Preferred embodiments of the invention will now be described, by
way of example only, with reference to the drawings, in which:

[0036]FIG. 1 shows a cross section of a solar window incorporating
optical elements for the collection and transmission of light.

[0064]FIG. 29 shows the fraction of incident light absorbed by the solar
cells as a function of the incident angle of the light entering the solar
cell window.

[0065] FIG. 30 illustrates a solar window in which lenses are employed as
optical elements.

DETAILED DESCRIPTION OF THE INVENTION

[0066] Generally speaking, the systems described herein are directed to
solar windows for the collection and regulated transmission of sunlight.
As required, embodiments of the present invention are disclosed herein.
However, the disclosed embodiments are merely exemplary, and it should be
understood that the invention may be embodied in many various and
alternative forms. The Figures are not to scale and some features may be
exaggerated or minimized to show details of particular elements while
related elements may have been eliminated to prevent obscuring novel
aspects. Therefore, specific structural and functional details disclosed
herein are not to be interpreted as limiting but merely as a basis for
the claims and as a representative basis for teaching one skilled in the
art to variously employ the present invention. For purposes of teaching
and not limitation, the illustrated embodiments are directed to solar
windows comprising optical elements and solar collecting elements for the
collection and regulation of sunlight.

[0067] As used herein, the terms, "comprises" and "comprising" are to be
construed as being inclusive and open ended, and not exclusive.
Specifically, when used in this specification including claims, the
terms, "comprises" and "comprising" and variations thereof mean the
specified features, steps or components are included. These terms are not
to be interpreted to exclude the presence of other features, steps or
components.

[0068] As used herein, the terms "about" and "approximately, when used in
conjunction with ranges of dimensions of particles, compositions of
mixtures or other physical properties or characteristics, is meant to
cover slight variations that may exist in the upper and lower limits of
the ranges of dimensions so as to not exclude embodiments where on
average most of the dimensions are satisfied but where statistically
dimensions may exist outside this region. It is not the intention to
exclude embodiments such as these from the present invention.

[0069] As used herein, the coordinating conjunction "and/or" is meant to
be a selection between a logical disjunction and a logical conjunction of
the adjacent words, phrases, or clauses. Specifically, the phrase "X
and/or Y" is meant to be interpreted as "one or both of X and Y" wherein
X and Y are any word, phrase, or clause.

[0070] Embodiments of the present invention provide a solar window
incorporating both solar collection and light regulation. Such a solar
window provides angular dependent regulation of light transmission, thus
preventing too much light from being transmitted during direct sun
conditions and increasing the fraction of light transmitted during
indirect sun conditions, while collecting the unwanted solar energy with
a solar collection element such as a solar cell.

[0071] A first embodiment is illustrated in FIG. 1, which shows a solar
window 10 having a transparent pane 20 that is preferably made of a
transparent material such as glass or thermopane glass. Adhered to an
internal surface 25 of pane 20 is a plurality of substantially
transparent optical elements 30.

[0072] Optical elements 30 comprise an externally facing surface 35 and an
internally facing surface 40. As shown in the Figure, the externally
facing surface preferably has a larger surface area than the internally
facing surface. This causes the concentration of incident sunlight onto a
light collecting element 70 adhered to the internally facing surface,
when the incident sunlight is provided over a first range of angles. The
concentration is caused by the reflection of incident rays by two or more
lateral light directing surfaces 50 and 55. The optical elements thus
increase the amount of light incident on each collection element and
decrease the required size of each collection element. This is
advantageous since the size of the collection elements may be reduced,
while still maintaining efficient solar collection in direct sun
conditions (for example, with reduced solar cell material cost). Optical
elements 30 are preferably formed from a transparent material such as
glass or acrylic, and are preferably bonded directly to pane 20. Direct
bonding improves heat transfer and reduces losses from additional Fresnel
reflections.

[0073] Each light directing surface 50 and 55 reflects incident rays over
a specific range of angles determined by the angle of the surface and the
index of refraction of the optical element. The rays are preferably
reflected by total internal reflection, although the reflectivity may be
produced at least in part by coating one or both of the light directing
surfaces with a coating that is at least partially reflective. It is to
be understood that light directing surfaces 50 and 55 need not be planar
surfaces, and may instead comprise curved or multi-faceted surfaces.

[0074] Rays 60 and 65 illustrate the case in which sunlight is normally
incident on pane 20, where the rays pass through the pane and are totally
internally reflected by surfaces 50 and 55 through the light collecting
surface 40. This scenario typically corresponds to a direct sun condition
would include angles of illumination when there are no clouds, and the
sun is at or near mid-day conditions. After passing through the light
collecting surface 40 of the optical element, rays 60 and 65 are
collected by light collecting surface 70.

[0075] Ray 75 illustrates a case in which sunlight is directed onto pane
20 at an oblique angle. This situation may arise when the solar altitude
is such that the ray is a direct ray and the sun is not near its peak
altitude, or alternatively the ray may originate as a scattered ray. This
could also occur as a sunrise or sunset condition. Ray 75 is refracted at
by pane 20 and propagates into optical element 30. Upon encountering
light directing surface 50, ray 75 is refracted outside of optical
element 30 and transmitted by surface 50. Similarly, ray 80 is refracted
by pane 20 and transmitted by element 30.

[0076] Solar window 10 therefore provides both solar collection and
regulated light transmission that varies as a function of the incident
angle. Advantageously, and unlike prior art designs, solar window 10
comprises two light directing surfaces 50 and 55 for selectively
transmitting or internally reflecting light rays that are incident from
both lateral directions. Each light directing surface transmits light
rays over a first incident angular range, and internally reflects light
rays over a second incident angular range.

[0077] In a preferred embodiment, solar window 10 further comprises a
second pane 5, which is secured to first pane 20 by member 15. Solar
window may therefore comprise a double-pane window that is sealed to
protect the optical elements 30 and additionally provides a low heat
transfer value. In a preferred embodiment, second pane optically diffuses
transmitted light. This is preferable as light transmitted through
optical elements 30 will have a spatial intensity variation that may be
desirably removed by a diffusing component integrated within solar cell
10. In non-limiting examples, diffusing component (not shown) may be
provided on a surface of second pane 20 or integrated within second pane
20.

[0078] The light collection element 70 comprises an element adapted for
the collection of light and the conversion of solar energy. In a
preferred embodiment, light collection element comprises one or more
solar cells. The solar cells are preferably mounted directly to the light
collecting surface 40 without an air gap to maximize the collected power.
In another embodiment, light collection element 70 comprises a light
absorbing material, such as a dark material that may be adhered to the
light collecting surface.

[0079] FIG. 2 shows overhead and cross-sectional views of optical element
30 according to one embodiment, in which optical element 30 comprises a
truncated square pyramid 85. In this embodiment, externally facing
surface 35 comprises the base of the pyramid, and light collecting
surface 40 comprises the truncated surface of the pyramid. The pyramid
further comprises two additional light directing surfaces 90 and 95. Dual
pairs of light directing surfaces are advantageous for modulating
transmitted light due to changes in solar altitude and azimuth. The
truncated pyramids are preferably arranged in an array, and more
preferably arranged in a two-dimensional array. Adjacent pyramids may be
in direct contact, or a gap may be provided to allow for increase light
transmission.

[0080] Those skilled in the art will appreciate that the pyramid shape and
geometry may be varied without departing from the scope of the invention,
for example, having different base geometries. Additionally, the pyramid
base may be additionally truncated at an angle, thereby allowing for
light collecting surface 40 to be tilted at an angle relative to pane 20.
Such an embodiment may be advantageous as it enables the light collecting
surfaces to be tilted to collect an optimal amount of solar energy. For
example, in a vertically mounted window, light collecting surfaces of
truncated pyramid optical elements could be oriented towards an average
seasonal solar inclination.

[0081] As noted above, in a preferred embodiment, light collecting
elements 40 are solar cells. FIG. 3 illustrates how an array of solar
cells may be connected for the extraction of electrical energy. An array
of solar cell chips 110 is shown connected to at least two wires 115 and
120. FIG. 3, illustrates an embodiment in which wire 115 is situated
below the chips 110, and wire 120 is situated above the chips 110,
whereby a voltage is generated between wires 115 and 120. The electrical
current and voltage from the chips 110 will contribute to the total
current and voltage. As will be apparent to those skilled in the art,
solar cell chips 110 may be connected in series, parallel, or a
combination thereof. FIG. 3 shows a series-parallel connection of the
solar cell chips 110. The wires may be contacted with the solar cell
chips by a variety of known methods, such as soldering the wires to the
solar cell chips or bonding the wires to the solar cell chips using
conductive cement. The wires are preferably made of a highly conductive
metal such as silver, copper or aluminum, and the wires are preferably
sufficiently rigid to be self-supporting between the solar cell chips. In
an embodiment involving two glass panes (as discussed above), the
electrical wiring may be externally routed through the window support by
suitable electrical connections that retain the seal for the gap between
the inner and outer glass plates.

[0082] In a non-limiting example, optical elements 40 were obtained by
cutting AFG Solite 5/32'' thick solar glass to form a truncated pyramid
150 as shown in FIG. 4. The light beam 160 was incident on the larger
surface of the truncated pyramid 150 as shown in FIG. 5. The small
surface of the truncated pyramid was covered by a light absorbing film
170.

[0083] The performance of the truncated pyramid was determined by
measuring the percentage of light transmitted through the truncated
pyramid as a function of the angle θ of the light incident 160 on
the truncated pyramid 150. The result is shown in FIG. 5. Note that when
θ=90°, which is an example of a direct sun condition, the
percentage of light transmitted is about 4% and when theta is 20°,
which is an example of an indirect sun condition, the percentage of light
transmitted has increased to over 25%.

[0084] In addition, measurements were made of electrical power available
from the same truncated pyramid as shown in FIG. 4 when a silicon solar
cell chip is substituted for the light absorbing film. This data was
measured as a function of θ as shown in FIG. 6. It is noteworthy
that power can be generated from a wide range of angles. If the same
solar cell chip is illuminated with the same light source but without the
truncated pyramid, then a much lower power is measured, as also shown in
FIG. 6.

[0085] FIGS. 7 and 8 illustrate a preferred embodiment in which optical
element 30 is a longitudinal transparent structure that is preferably a
prism. Shown in FIG. 7 are the various surfaces of the prism, including
externally facing surface 205, light collecting surface 210, and light
directing surfaces 215 and 220. Accordingly, prism 200 has a transverse
cross-section as shown in FIG. 1.

[0086] Preferably, the solar window comprises a one-dimensional array of
longitudinal prisms, as shown in FIG. 8. Solar window 250 comprises
transparent pane 260 and a plurality of longitudinally oriented prism.
Shown in the Figure are light collection elements 270 adhered to light
collecting surfaces of the prisms, and light directing surfaces 215 and
220. While adjacent prisms are shown in mutual contact, it is to be
understood that a lateral gap may be provided to increase the
transmission of light through the structure. Furthermore, one or both
ends 280 of each prism may be cut at an angle relative to a plane
orthogonal to a longitudinal axis of the prism.

[0087] As discussed above, the optical collection elements 270 adhered to
the light collection surfaces 210 are preferably solar cells. FIG. 9
shows the manner in which solar cells may be connected for the embodiment
shown in FIG. 8. An array of solar cell elements 300 is shown, where each
solar element is connected to at least two wires 305 and 310. In the
Figure, wire 305 is situated below the solar cells 300, and wire 310 is
situated above the solar cells 300. Accordingly, a voltage is generated
between wires 305 and 310. The electrical current and voltage from the
elements 300 will contribute to the total current and voltage.

[0088] FIG. 9 shows a parallel connection of the solar cell elements,
although it will be clear to those skilled in the art that the solar cell
elements could also be connected in series or in a series/parallel
arrangement. As noted above, the wires may be connected to the solar
cells using one of many means, including soldering the wires to the solar
cell elements using solder or bonding the wires to the solar cell
elements using conductive cement. The wires are preferable made of a
highly conductive metal such as silver, copper or aluminum. FIG. 9 shows
only one solar cell element for each long solar cell length, however two
or more suitably connected solar cell elements could be used to increase
the effective length of the solar cells. In an embodiment involving two
panes (as discussed above), the electrical wiring may be externally
routed through the window support by suitable electrical connections that
retain the seal for the gap between the inner and outer glass plates.

[0089] Although the optical elements shown in FIGS. 7 and 8 are isosceles
trapezoidal prisms, it is to be understood that the prisms can take on a
wide variety of geometries without departing from the scope of the
invention. The prisms preferably include at least four lateral sizes,
with a first side comprising the externally facing surface, a second side
comprising the light collecting surface, and at least two additional
light directing surfaces, where the light directing surfaces are
preferably located on either side of the prism. The prism is preferably a
quadrilateral prism, and more preferably, a trapezoidal prism. The light
directing sides of the prism need not be planar surfaces, and may instead
comprise curved or multi-faceted surfaces.

[0090] FIGS. 10-27 provide results from a simulation involving the
non-limiting embodiment shown in FIG. 8. The collection and transmission
of sunlight incident on the solar window was simulated through optical
ray tracing software (Optic Lab). The optical path of the incident light
beam at various incident angles is analyzed over three modes. In a first
mode, the incident angle ranges from 0 degrees to 25°, and the
light path is illustrated in FIGS. 10 to 15, where the incident angle is
increased from 0 to 25° in steps of 5°. In FIG. 10, the
sunlight entering the window is shown at 350, and most of the sunlight
reaches the solar cell elements 360. The light being transmitted through
the window is shown at 370. For simplicity, the first and second panes 20
and 5 are not shown in the Figures. The incident angle is measured as the
angle between the incident light beam and the normal to the solar window
surface. The modeling is two dimensional.

[0091] In a second mode, the incident angle ranges from 30° to
40° degrees and the light path is illustrated in FIGS. 16 to 18.
In this intermediate mode, a portion of the light transmitted into the
optical elements is directed to the solar cells, and another portion is
refracted and transmitted by the light directing surfaces. In a third
mode, the incident angle ranges from 45° to 85°, and the
light path is illustrated in FIGS. 19 to 27. In this transmissive mode,
most of the light transmitted into the optical elements is refracted and
transmitted by the light directing surfaces. It is noted that in all
three modes, light is directed either to the solar cells or through the
window.

[0092] FIG. 28 shows the calculated fraction of the incident light that is
transmitted through the solar window as a function of the angle of light
incidence, and FIG. 29 shows the fraction of the incident light that is
collected by the solar cells as a function of the angle of light
incidence. At 0 degrees, 30% of the light is transmitted through the
window and 70% of the light reaches the solar cells. As the incident
angle is increased, the percentage of transmitted light monotonically
increases, until full transmission is achieved for angles in excess of
approximately 4 degrees (not including losses due to Fresnel
reflections).

[0093] It should be noted that the computer modeling does not take into
account optical effects such as absorption losses in the optical
materials, and surface reflections. In addition, the influence of the
inner glass which could be a diffusing glass sheet has not been included,
and three dimensional modeling rather than the two dimensional used would
be needed to obtain more precise results.

[0094] FIGS. 28 and 29 highlight the unique functionality of the solar
windows according to various embodiments of the invention, where the
transmitted light is bi-modally modulated on either side of the minimum
transmission direction. This feature is achieved by the incorporation of
at least two light directing surfaces in the optical element. Each light
directing surface provides transmission for a range of angles on either
side of the angle of normal incidence.

[0095] This feature provides a significant benefit when a solar window
according to an embodiment of the invention is oriented in selected
geometries. If the solar window is oriented such that (a) the optical
elements can receive direct sunlight and (b) the optical elements have
their longitudinal axis directed approximately within a plane that
includes a single line of longitude, then the daily time-dependent
transmission of sunlight through the solar window has a trend that is
opposite to that of the intensity of sunlight directed onto the window.
This has the benefit of reducing the amount of light transmitted during
peak hours of sunlight, and the reduced light is advantageously received
by the collection elements for solar energy conversion. It is important
to note that this benefit can be obtained for solar windows installed in
a wide range of configurations, including both horizontal windows, such
as skylights, and vertical windows.

[0096] An additional benefit is also obtained when the solar window is
further oriented to account for seasonal changes in solar altitude. If
the solar window is oriented such that the minimum transmission occurs
during the summer season, then an increase in transmission will be
obtained during the winter season. This can be beneficial in regulating
the amount of light transmitted into a building to optimize the
internally transmitted heat during the winter and minimize the amount of
internally transmitted heat during the summer.

[0097] In another embodiment of the invention, the solar window apparatus
as described in various embodiments herein may comprise a retrofit kit
that includes fasteners such as mounting screws, suction devices, or
other hardware for securing the pane 20 to an internal surface of an
existing window.

[0098] Referring again to FIG. 1, light collecting elements 70 are mounted
along with the optical elements 30 to transparent pane 20 and do not
contact second pane 5. This may be advantageous in warm climates where
air conditioning is required to maintain indoor air temperature since the
second pane 5 does not directly contact the light collecting elements,
and therefore less air conditioning would be required. For example, since
solar cells heat up in sunlight, the temperature rise of the inner glass
in warm climates will be reduced by the insulation provided by the space
between panes 5 and 20.

[0099] It should also be realized, however, that the solar cells will be
heated by the sun, which will decrease the solar cell performance for
silicon solar cells. Accordingly, in embodiments in which light is
collected by a light collection element adhered to each optical element,
a means of heat transfer is preferably included for conducting heat away
from the light collection elements. Such a heat transfer means may be
implemented for ensuring that solar cells are operating efficiently
and/or extracting useful thermal energy collected by the solar window
(for example, if light collection element is a light absorbing material).
In one embodiment, the heat transfer means may comprise a heat sink in
thermal communication with the light collecting elements. In a
non-limiting example, the heat sink may comprise a conductive rod
provided below each longitudinal optical element shown in FIG. 8.
Alternatively, the heat sink may comprise a liquid conduit for flowing a
liquid, where the conduit provides direct or indirect thermal
communication between the light collecting elements and the fluid.
Preferably, liquid is flowed through the conduit using a flow means such
as a pump. In selected embodiments in which the conduit is exposed to
incident light, the conduit and working liquid are preferably
substantially transparent.

[0100] In another embodiment of the invention, light directing surfaces
may further comprise a partially reflective material for increasing the
surface reflectivity. Additionally, a reflective material may be
substituted for the light collecting element to provide a solar window
that regulates transmission without collecting solar energy. The
reflective material substituted for the light collecting element may be
partially or fully reflective.

[0101] In yet another embodiment, the solar window may provide light
regulation and without light collection, where the optical element
comprises a prism having at least two light directing surfaces, whereby
the light collecting element and light collecting surface are absent.
Light incident on the solar window over a first range of angles is
externally reflected through total internal reflection and light incident
on the window from a second range of angles is transmitted. In a
preferred embodiment, the prism comprises a triangular prism for light
regulation by total internal reflection.

[0102] FIG. 30 provides an alternative embodiment of a solar window 400 in
which the optical elements of FIG. 1 are replaced with lenses 410. Lenses
preferably comprise a flat surface for ease of mounting to external pane
420. Preferred lenses include, but are not limited to, plano-convex
lenses, and diffractive elements such as Fresnel lenses. Light collecting
elements 430 are supported on externally-facing surface 440 of internal
pane 450. Preferably, internal surface 450 is positioned near a focal
plane of lenses 410, and each light collecting element 430 is positioned
at a focal point of a given lens 410. Accordingly, light incident from a
first range of angles 460 is directed by lenses 410 onto light collecting
elements 430, and light incident from a second range of angles 470 is
transmitted though internal pane 450. Preferably, internal pane 450
diffuses transmitted light 480. Such an embodiment may be useful in cold
climates, whereby light collection elements 430 mounted on internal pane
450 provide a temperature rise that could also provide heat to internal
pane 450.

[0103] It is to be understood that the geometry and location of the
optical elements and their relative location on the pane may preferably
be selected to account for the thermal conditions including the solar
cell temperature and window heat transfer, and to obtain a desired
optical performance including window light transmission as a function of
light angle, and on the electrical performance required. For example,
optical elements may be spaced apart with a gap therebetween to allow for
increase light transmission. Those skilled in the art of solar cells and
window design will readily appreciate that design variants involving the
aforementioned principles and examples are within the scope of the
present embodiments.

[0104] The foregoing description of the preferred embodiments of the
invention has been presented to illustrate the principles of the
invention and not to limit the invention to the particular embodiment
illustrated. It is intended that the scope of the invention be defined by
all of the embodiments encompassed within the following claims and their
equivalents.